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Reply-To: "Doobs" <doobs@doobs.com>
From: "Doobs" <doobs@doobs.com>
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References: <LIednWDbPNgXGbPZRVnysQ@pipex.net>
 <87odzl5ilt.fsf@mid.deneb.enyo.de>
 <SdmdndA2Z9jbI7PZnZ2dnUVZ8qWdnZ2d@pipex.net>
Subject: Re: Any way of persuading GNAT/GCC to implement a true overlay and
 not a pointer?
Date: Sat, 1 Apr 2006 19:19:48 +0100
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Date: 2006-04-01T19:19:48+01:00
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"Doobs" <doobs@doobs.com> wrote in message 
news:SdmdndA2Z9jbI7PZnZ2dnUVZ8qWdnZ2d@pipex.net...
>
> "Florian Weimer" <fw@deneb.enyo.de> wrote in message 
> news:87odzl5ilt.fsf@mid.deneb.enyo.de...
>>> I was under the impression that code of the following form :
>>>
>>> X : <Some Type>;
>>> Y : <Some Type>;
>>> for Y'Address use X'Address;
>>>
>>> would result in an overlay in the resulting code.
>>
>> Could you show some more code?  Probably initialization is causing
>> your problems, which can be fixed with a pragma Import.
>
> The following is an example of the problem:
>
> package TestPackage
> is
>
>   type MyRecordType is
>   record
>      element1 : Positive;
>      element2 : Positive;
>   end record;
>
>   type MyArrayType is array(1..2) of Positive;
>
>   myX : MyRecordType;
>   pragma volatile(myX);
>   myY : MyArrayType;
>   pragma volatile(myY);
>   for myY'Address use myX'Address;
>
>
> end TestPackage;
>
> The following fragments of the resulting MAP file (GCC 3.4.2 mingw32) show 
> the problem...
>
> .data          0x00472b00       0x10 ./testpackage.o
>                0x00472b00                testpackage__myy
> .data          0x00472b10       0x10 ./nextpackage.o
>
> <..... later in the file...>
>
> COMMON         0x004a2770       0x20 ./testpackage.o
>                0x004a2770                testpackage__myx
>                0x004a2780                testpackage_E
>
>
> Clearly myX and myY do NOT share the same address.  I am also puzzled as 
> to why the variables have been put in differen memory sections...
>
Note that including a pragma import did NOT solve the problem - the code 
looked like this

   myX : MyRecordType;
   pragma volatile(myX);
   myY : MyArrayType;
   pragma volatile(myY);
   for myY'Address use myX'Address;
   pragma Import (Ada, myY);


But the map file exhibited the same problem as before.